The present application relates to the field of object recognition, and in particular to object recognition techniques that utilize ionizing radiation to determine one or more physical characteristics and/or morphological characteristics of an object under examination. It finds particular application in the context of security imaging where it may be desirable to identify potential threat items concealed within an object (e.g., a suitcase, purse, human, etc.). However, it may also find applicability in medical fields, industrial fields, and/or other fields where radiation imaging modalities are employed to examine and/or image an object.
Today, radiation imaging modalities such as computed tomography (CT) systems, single-photon emission computed tomography (SPECT) systems, projection systems, and/or line-scan systems, for example, are useful to provide information, or images, of interior aspects of an object under examination. Generally, the object is exposed to radiation comprising photons (e.g., x-rays, gamma rays, etc.), and an image(s) is formed based upon the radiation absorbed and/or attenuated by interior aspects of the object, or rather an amount of radiation photons that is able to pass through the object. Generally, highly dense aspects of the object absorb and/or attenuate more radiation than less dense aspects, and thus an aspect having a higher density, such as a bone or metal, for example, may be apparent when surrounded by less dense aspects, such as muscle or clothing.
Radiation imaging modalities are utilized in a variety of fields to examine and/or image aspects of an object not readily visible to the naked eye. For example, radiation imaging modalities are used in security applications to identify potential threat items, such as weapons and/or explosives that may be concealed within a suitcase, bag, or person, for example. Two of the more commonly used radiation imaging modalities in security applications are CT systems and line-scan systems. Line-scan systems are configured to view the object from a limited number of angles and generate projection images (e.g., two dimensional images) respectively representing a collapsed or flattened, two-dimensional view of the object (e.g., where the densities of various items along a line in which radiation travels are integrated and represented as a single point on the image). CT systems are configured to view an object from a plurality of angles (e.g., at least 180 degrees but often 360 degrees) to generate volumetric data representative of the object. In this way, a 3D image of the object can be created and properties of respective items within the object, such as density information, Z-effective information, shape characteristics, etc. can be determined based upon data indicative of the 3D image.
In some embodiments, data generated from an examination of an object is analyzed by the radiation imaging modality using automatic threat analysis algorithms to determine if the object comprises a potential threat item and/or other item of interest. For example, the radiation imaging modality may analyze a projection image generated by a line-scan system to determine if an outline of a weapon can be identified and/or may analyze data related to a three-dimensional image generated by a CT system to determine if an organic explosive is potentially comprised within the object.
While automatic threat analysis algorithms have proven useful to identify potential threat items and/or other items of interest, such algorithms may, at times, mischaracterize an item, resulting in a false positive. In a security application this may result in non-threat items being incorrectly classified as a potential threat item. Accordingly, objects flagged as comprising a potential threat item and/or other item of interest may have to be resolved by some other method(s), such as a visual inspection of image(s), hand search of the items, and/or via use of some other screening technology.